The reactivity of N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)-L-histidine towards copper(II) ions

The acid-base properties of the N-substituted amino acid HL [HL = N-2-(4-am ino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)-L-histidine] and its r eactivity towards the Cu-II ion have been measured by potentiometric and sp ectrophotometric techniques in aqueous solution at 25 degreesC and 0.1 M KC l ionic strength. These studies show that the neutral HL compound is presen t in aqueous solution (3-7 pH range) in the zwitterionic form with the dipr otonated imidazolic residue. Studies of HL/Cu-II mixtures reveal the existe nce of complex species with the neutral ligand, HL and containing the depro tonated L ligand. By controlling the reaction conditions, four solid phases of stoichiometry: CuLCl(H2O)(6), Cu2LCl3(H2O)(8), CuL2(H2O)(6) and Cu(HL)( 2)Cl-2(H2O)(6) were isolated and characterised by i.r. and electronic spect roscopy, thermal techniques and magnetic measurements.